Compressor load protector



Nov. 30, 1948.

C. E. PLOEGER COIPRESSOR LOAD PROTECTOR Filed Sept. 7. 1946 Patented Nov; 30, 1948 Y comassoa Loan rao'rscroa Clyde E. Ploeger, Evansville, 1nd., assignor to Sei-vel, Inc., New York, N. Y., a corporation of Delaware Application September '1, 1946, Serial No. `695,452

- This invention relates to load protectors for electric motors, and particularly to protectors g for electric motors used for driving the compressor of a refrigerating system of the compressorcondenser-expander type.

In my prior Patent No. 2,043,058, granted .lune

2, 1936, I disclose a magnetic unloader to relieve an electric motor of its load at starting and to keep the load relieved until the motor has attained the requisite' speed. 'I'his prior unloader, which is operated bythe leakage magnetic field of the motor, and which opens an unloading valve at starting 'and closes the unloading valve when the leakage neld decreases, operates very satisfactorily as far as it goes. However, my prior invention protects the electric motor against starting loads only. That is, the unloading valve is either fully open or fully closed depending upon whether the motor is just starting or whether it has attained the requisite speed.

The present invention contemplates a device for protecting electric motors against running loads aswell as against starting loads. So far as Q I am aware, compressor unloading devices have not been controlled directly by the flux' current of the motor for governing the running load.

Bpeciiically, my motor protector comprises a lvalve in the suction line between the expander and the compressor of a refrigerating system. This valve is conveniently vpositioned within the motor-compressor housing of an hermetically sealed unit and includes a member constructed of magnetic material so positioned and arranged with respect to the motor that it is attracted by the leakage magnetic iield to close the valve at starting, which valve is opened as by springs as the leakage field decreases as the motor comes up to speed. The valve is so positioned relative to v the motor stator and rotor that it floats back and forth depending upon the intensity of the magnetic leakage ileld. At starting, the leakage field www. (ci. aso-24) i The use of my improved unloader enables a motor compressor unit to be more heavily loaded in that the running load and the displacement of the compressor can be balanced at the design or operating point. Heretoforethe displacement has had\to be adjusted lower softhat the maximum overload or pull-down conditions will not be beyond the capacity of the motor.

- This invention will be more fully understood by reference to the following description taken inconnection with .the accompanying drawing wherein: A Y

' Fig. 1 isa view partly in section of the motor end of a motor-compressor unit `incorporating myv invention; n

Fig. 2 is a view similar to Fig. 1 but showing my improved unloader valve in full open position;

Fig. 3 is a transverse sectional View taken on line 2-3 of Fig. l.

Referring to the drawing, an hermetically sealed casing i0 encloses a motor-compressor unit of a refrigerating system. The particular type of compressor that is employed in the refrigerating system forms no part of this invention, therefore only the motor end of motorcompressor unit is illustrated. As shown, an electric induction motor comprising a stator l2 and rotor il having an air gap i4 therebetween isarranged within the casing. The stator may be Vsecured within the casing in any suitable manner vas by a shrink fit. The casing is provided with a Y removable head IB upon which is mounted my improved motor protector designed generally `by reference numeral I8.

This motor protector includes an annular mounting plate 2li hermetically secured to the head of the casing as by screws 22 and having a cylindrical valve cup 24 hermetically secured thereto. An annular flux ring 26 made of magnetic material is mounted for axial sliding moveis of maximum intensity and the valve is drawn v to closed position. Then, as the rotor approaches running speed and the leakage ileld decreases,

the springs gradually open the valve admitting.

refrigerant vapor to the compressor. Then, with the motor running normally, the valve remains open. If, however, the motor iswsuddenly overloaded as by an overload applied to the compressor thevalve is drawn to closed or partly closed position depending upon the load. In other words, the valve is in fully open position only so long as a normal load is applied to the compressor and the rotor is operating substantially at lull speed.

Vment upon the cup 24 and together with the cup forms a valve for controlling the flow of re'- frigerant vapor through an opening 28 in the head of the casing, which opening is connected by a suitable conduit, not shown, to the` suction side of the expander of the refrigerating system. Inward movement of the flux ring is limited by a stop plate 30 secured to the valve cup by screws 32. Four equally spaced guide bolts 34 provided with compression springs 36 are mounted between the mounting plate 20 and the stop plate 30. In order that a universal unloader may be used fordiiferent size motor-compressor units, suitable means, not shown, may be provided for adjusting the springs 38. As shown, the ux ring is provided with a cylindrical sleeve 28a which lits snugly upon the valve cup 24 for axial movement relative thereto. This sleeve is provided with a plurality oi' ports 38 which cooperate with a like plurality of ports l in the valve cup ior admitting refrigerant vapor to the compressor. A line mesh strainer I2 is mounted in the valve cup.

In operation, as above described, the magnetic ileld of the motor is greatly distorted at the instant of starting and consequently the magnetic ring 28, the inner end of which is positioned adjacent the rotor of the motor, is attracted and moved to the right from the position shown in Fig. 2 to that shown in Fig. 1, thereby moving the valve ports 38 and 49 out of register and closing the valve, thus taking the load off the compressor. The magnetic ring will remain in this attracted position until such time as the rotor picks up speed and the leakage flux has decreased to the extent that the force of the compression springs is suillcient to gradually move the' magnetic ring to the left bringing the valve ports into register, whereby refrigerant vapor is drawn from the suction line through the opening 28, through the ports 40 and 38 and through the gap between the motor stator and rotor and into the compressor, not shown, thus the compressor is gradually loaded. As the rotor comes up to speed the current in the motor windings decreases and the leakage field diminishes whereby the springs draw the magnetic ring to the position shown in Fig. 2 with the valve in fully open position and the compressor fully loaded. 'I'he valve remains in the open position shown in Fig. 2 so long as the motor-compressor unit operates normally. If, however, an abnormal load is applied to the unit, as by a sudden overload on the expander of the refrigerating system, which overload is applied to the compressor and from there to the motor, a magnetic field leakage is created which attracts the magnetic ring, thus partly closing the valve and reducing the load on the compressor. In this manner the magnetic ring ii'oats back and forth opening and closing the valve to a greater or less degree in accordance with the load placed upon the motor.

Although but one specific form of my invention has been illustrated and described and this specic form has been incorporated in a motorcompressor unit of a refrigerating system of the compressor-condenser-expander type, my invention obviously may take other forms and be variously applied. The invention is therefore limited only as defined in the claims.

Having thus described my invention, I claim;

1. In combination a compressor, an electric motor for operating said compressor, a valve connected to said compressor for varying the load thereon, said valve being provided With a member constructed of magnetic material disposed within the magnetic leakage field of said motor to be attracted thereby for moving said valve in one direction, means opposing the attraction of the magnetic leakage iield urging said valve in the opposite direction, the construction and arrangement being such that when the magnetic leakage eld is of maximum intensity, as at the instant of starting the motor, the valve is moved in one direction to unload the compressor and as the motor approaches running speed the valve is moved in the opposite direction to load the compressor, thereafter during operation of the compressor the valve modulates between open and closed positions in accordance with the intensity of the magnetic field as reflected by the load on the compressor.

2. In combination a compressor, an electric motor for operating said compressor, an unloading valve in the suction side oi' said compressor, saidvalve being provided with a member constructed of magnetic material disposed within the magnetic leakage field of said motor to be attracted thereby for closing said valve, means opposing the attraction of the magnetic leakage field urging said valve toward open position, the construction and arrangement being such that when the magnetic leakage field is of maximum intensity, as at the instant of starting the motor, the valve is closed and as the motor approaches running speed the valve is urged toward open position, thereafter during operation of the compressor the valve modulates between open and closed positions in accordance with the intensity of the' magnetic ileld as reflected by the load on the compressor.

3. In combination an electric motor, a cornpressor operatively connected to the motor in such manner as to place a load upon the motor thereby causing a magnetic leakage eld of varying intensity to be set up in the motor, means utilizing the intensity of the magnetic leakage eld for governing the load placed upon the motor, said means including a valve connected to the compressor, said valve having a portion thereof disposed within the magnetic leakage ield to be attracted thereby for moving the valve in one direction, means opposing the attraction of the magnetic leakage ileld urging the valve in an opposite direction, the construction and arrangement being such that when the motor is running and the load on the .compressor is increased the valve is moved in one direction thereby decreasing the load on the motor and as the m-otor approaches running speed the valve is gradually moved in an opposite direction increasing the load on the motor.

4. In combination an electric motor, a compressor operatively connected to the motor in such manner as to place a load upon the motor thereby causing a magnetic leakage field of varying intensity to be set up in the m-otor, means utilizing the intensity of the magnetic leakage ileld for governing the load placed upon the motor, said means including a valve in the suction side of the compressor, said valve having a portion thereof disposed within the magnetic leakage field to be attracted thereby for moving the valve toward closed position, means opposing the attraction of the magnetic leakage eld urging the valve toward open position, the construction and arrangement being such that when the motor is running and the load on the compressor is increased the valve is partly closed thereby decreasing the load on the motor and as the motor approaches running speed the valve is gradually opened.

CLYDE E. PLOEGER.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,912,463 Ploeger June 6, 1933 2,043,058 Ploeger June 2, 1936 2,043,059 Ploeger June 2, 1936 

